Operation of an internal combustion engine normally includes the burning of a combustible mixture comprising a fuel, together with a combustion supporting gas. Among the most common mixtures is a carbonaceous fuel, plus atmospheric air. The combustible mixture is rapidly burned in a combustion chamber whereby to displace a moving element such as a piston or the like on a power stroke. Concomitant with such burning, the resulting exhaust gases will normally be muffled, and discharged to the atmosphere. To minimize the degree of atmospheric pollution caused by the indiscriminate discharge of these exhaust gases, various governmental agencies, as well as industry in general, have determined to decrease the amount of such discharge.
Among the more noxious of the air polluting gases discharged to the atmosphere are the various oxides of nitrogen. These are generally referred to hereinafter, as well as in the industry as NO.sub.x.
While not the most detrimental of the substances discharged into the atmosphere, NO.sub.x does account for a large proportion of the total engine emission gases. Further, it depends for its potency as a pollutant on the character of the particular combustion, and the composition of the fuel burned.
To substantially reduce and even eliminate the amount of NO.sub.x discharged to the atmosphere from an engine of the internal combustion type, the present method and apparatus are provided. In essence, the instant method comprises the sequential segregation of and recycling of a minor portion of the total exhaust gas stream created in the engine. Said segmented portion, although it does not support combustion, is intimately mixed with another combustion supporting gas to form a preliminary mixture.
The preliminary gaseous mixture is thereafter introduced into a combustion chamber together with a predetermined amount of fuel, either in liquid or gaseous phase. The forced intermingling of the latter with a portion of the preliminary mixture, provides a combustible fluid that is thereafter ignited by positive sparking action, or by other suitable vehicle.
To achieve the noted objectives, the invention more specifically comprises a method for operating an engine in which a fuel is rapidly burned in the presence of a combustion supporting medium. The latter, however, comprises a major portion of air and a minor portion of cooled, recycled exhaust gas. Characteristic of the exhaust gas, is in the physical property of its being highly adsorbent of heat, and further does not take part directly in the combustion process. The overall result of this type burning is that the temperature within a combustion chamber will be substantially reduced. Further, with low temperature combustion, there will be a substantial reduction in, or complete elimination of NO.sub.x which might otherwise hav occurred with an ordinary air/fuel mixture.
The apparatus of the invention is directed to the system, or means for achieving the circumstances in the engine combustion chamber which results in the desired burning. Said means further comprises a control arrangement whereby the amount of exhaust gas which is recycled into the combustion chamber is varied in accordance with the load imposed upon the engine. In effect the flow of heated recycled exhaust gas is varied in accordance with the throttle position such as to vary the volume of exhaust gas recycled, from a maximum of approximately 30% by volume, at idle speed, to a minimum of approximately 15% by volume under loaded conditions.